The present invention relates to a method for making alkylhalosilanes. More particularly, the present invention relates to a process involving the reaction of methyl chloride and powdered silicon in the presence of a copper chloride catalyst and a minor amount of fumed silica.
As taught by Rochow, Chemistry of the Silicones, Second Edition, John Wiley & Sons (1951), Cuprous Chloride, can be deposited on the grains of silicon by reduction to provide a reactive contact mass for the synthesis of chlorosilanes from methyl chloride and powdered silicon. Those skilled in the art know that cuprous chloride has a tendency to sinter when heated to temperatures exceeding 230.degree. C., which interferes with its use as an attractive copper source for the direct method of making methylchlorosilanes in a fluid bed reactor. It has been known, for example, that "clumping" or caking of the mixture of cuprous chloride and powdered silicon can occur in the fluid bed which can interfere with the performance of the resulting copper-silicon contact mass in converting methyl chloride and powdered silicon to methylchlorosilanes. Agglomeration of the cuprous chloride powdered silicon contact mass can be alleviated to some extent by mechanical agitation, such as provided by a stirrer. However, agglomeration of the cuprous chloride-powdered silicon mixture prior to the formation of copper-silicon contact mass in the fluid bed can seriously interfere with fluid bed performance. It would be desirable to be able to use cuprous chloride as a source of copper in a fluid bed reactor as other forms of copper compounds, such as copper oxide, can be used.
The present invention is based on the discovery that a mixture comprising powdered silicon, fumed silica and cuprous chloride fed intermitently or on a continuous basis to a fluid bed reactor can result in no caking. Evidence of clumping in a fluid bed reactor when it is running under continuous conditions can be shown by irregular hot spots as detected with thermocouples.